Zinc, with its silvery-white metallic luster, quietly permeates every aspect of modern life: the galvanized coating
that protects steel, zinc alloys that power machinery, and trace elements essential for health... However, this brilliance
is not innate; it originates from deep within the ore, undergoing a complex transformation known as “smelting.”
This article will delve into the core processes and cutting-edge technologies of modern zinc smelting, unveiling
the mysteries behind the birth of metallic zinc.
The Ore's “Metamorphosis”: Ore Dressing and Pre-Treatment
Zinc does not exist in its pure form in nature; it is primarily found in sulfide minerals such as sphalerite. The first step
in smelting is to extract zinc from the ore:
Essentials of Mineral Processing: After crushing and grinding the raw ore, zinc minerals are separated from gangue
using their differing physical and chemical properties (such as density and surface characteristics) through techniques
like flotation. The final product—zinc concentrate—can achieve a zinc content of over 50%, laying the foundation for
efficient smelting.
Pre-treatment key: Zinc sulfide concentrate typically requires roasting treatment. In a precisely controlled fluidized
bed roaster (temperature approximately 900–1050°C), the zinc concentrate reacts with oxygen to form zinc oxide,
which is soluble in dilute acid, while releasing sulfur-containing flue gas. Efficiently collecting and converting these
fumes into sulfuric acid has become a standard practice in modern smelting plants for environmental protection
and resource recycling.
The Two Giants of Smelting Processes: The Rivalry Between Pyrometallurgy
and Hydrometallurgy
From zinc concentrate to metallic zinc ingots, the current mainstream processes are divided into two main pathways:
“pyrometallurgy” and “hydrometallurgy,” each with its own advantages.
Pyrometallurgy: Tradition and Challenges
Core Principle: The core lies in high-temperature reduction. Pre-treated zinc oxide (or sintered blocks) is mixed with a
carbon-based reducing agent (coke) and heated to over 1000°C in a sealed blast furnace or electric furnace. Zinc is
reduced to vapor (boiling point 907°C) and discharged along with the furnace gas.
Condensation Challenges: The rapid and efficient condensation of gaseous zinc is critical to success. Modern technology
primarily employs lead rain condensers, where molten lead is sprayed to absorb zinc vapor, followed by separation in a
settling tank based on density differences to achieve pure separation of zinc and lead.
Limitations: Pyrometallurgy has relatively limited adaptability to raw materials, high energy consumption, and difficulty in
economically recovering associated metals, posing challenges in terms of environmental protection and resource
utilization efficiency.
Hydrometallurgy (electrolytic method): The mainstream choice
Leaching Core: This is the starting point of the wet process. Roasted zinc oxide (zinc oxide) is leached using dilute
sulfuric acid solution, with zinc entering the solution in the form of zinc sulfate, while impurities such as iron and
silicon form leaching residue. Multi-stage leaching (neutral, acidic, hot acidic) and potassium iron sulfate methods
are commonly used to maximize zinc recovery rates and control impurities.
Solution Purification: The leaching solution contains various impurity ions (such as copper, cadmium, cobalt, and
nickel), which must be thoroughly purified to ensure electrolytic quality. Through a combination of zinc powder
replacement and organic solvent extraction, impurities are precisely removed, yielding high-purity zinc sulfate
electrolytic solution.
Electrolytic Deposition: The purified solution enters the electrolytic cell, with aluminum plates as the cathode and
lead-silver alloy as the anode. Upon electrification, zinc ions precipitate at the cathode to form dense zinc plates
(zinc ingots), while oxygen is released at the anode. Current efficiency and energy consumption are the core
economic indicators of this process. The cathode zinc produced is melted and cast to obtain high-quality
zinc ingots (>99.995%).
Advantages: The wet process has strong adaptability to raw materials, high zinc recovery rates (>95%), excellent
product purity, and can effectively recover multiple valuable metals such as cadmium, cobalt, copper, and silver.
It also has superior environmental performance and has become the absolute mainstream in global zinc smelting.
Circulation and Renewal: The Green Return of Waste Zinc Resources
The lifecycle of zinc extends far beyond a single smelting process. The recycling of zinc-containing waste materials
(such as galvanized steel, die-cast zinc alloys, and zinc slag dust) is of critical importance:
Recycling Value: The energy consumption of recycled zinc is only 20-30% of that of primary zinc, significantly
reducing resource consumption and environmental impact.
Recycling Processes: Depending on the form of the scrap, processes such as remelting and refining (for clean scrap),
distillation (for zinc-containing dust), or wet leaching (for zinc-containing slag sludge) are employed to rejuvenate
zinc and reintegrate it into the supply chain.
Technological Frontiers: Advancing Toward Greater Efficiency and Cleanliness
Zinc smelting technology has never ceased to evolve, with a clear focus on innovation:
Environmental Upgrades: Stricter emission standards drive technological innovation. Breakthroughs continue
in areas such as oxygen-enriched smelting, harmless treatment and resource recovery of leaching residues (e.g.,
recovery of silver, lead, and indium), and advanced wastewater treatment and near-zero emissions technology.
Energy Efficiency Enhancement: Optimizing process flows (such as thermal acid leaching-iron sulfate iron removal),
developing energy-saving equipment (such as high-efficiency electrolytic cells), and applying waste heat recovery
systems (recovering thermal energy from roasting, smelting, and other processes) significantly reduce energy
consumption per unit.
Maximizing Resource Utilization: Technologies for economically and efficiently extracting rare and precious metals
such as germanium, indium, and gallium from complex raw materials and smelting by-products have become a
key battleground for enhancing overall efficiency.
Intelligent Empowerment: Automation control, big data analysis, and artificial intelligence are increasingly being
applied to process optimization, fault prediction, and quality control, enhancing production stability and efficiency.
Conclusion:
From dormant ore to the silver cornerstone supporting modern industry, the zinc smelting journey is a profound
transformation blending chemical ingenuity, engineering expertise, and environmental responsibility. Wet smelting,
with its exceptional efficiency and environmental advantages, has become the dominant force in the industry, while
ongoing technological innovation continues to drive this ancient industry toward a cleaner, smarter, and more
sustainable future. Whether it is galvanized steel sheets protecting buildings or zinc-based batteries powering
the future, every application of zinc embodies the refinement and evolution of smelting technology. Understanding
this journey allows us to more deeply recognize the foundational role and future potential of this basic metal in the
development of human civilization.